FIGURE 3.

Concurrent Model for proprioceptive assessment tasks. Sensory inputs from the target and the effector are concurrently compared in four reference-frames: retino-centered (ΔR), joint-centered (ΔJ), extra-retinal (ΔExR), and extra-joint (ΔExJ). The visual (red) and proprioceptive (blue) signals are primarily encoded in retino-centered and joint-centered reference frames, respectively, but they can also be encoded in additional “secondary” reference frames not directly associated with the respective receptors. To encode a sensory signal in a secondary reference frame, cross-reference transformations (represented by the curved green arrows) are necessary.